Methods and devices for monitoring IntraCranial Pressure (ICP) and brain density variations are highly valued for diagnosis and assessment of various ailments including head injuries, hemorrhage, variations of blood flow in the skull due to drug effects, changes in brain temperature and variations in metabolism and stress. Elevated ICP is a pathological condition of a patient and an indicator of neurological damage and illness. Numerous pathological conditions cause the matter within the skull to increase, but the inability of the skull to expand significantly causes the ICP to increase exponentially with increasing matter. A primary concern caused by an elevated ICP is brain herniation. The brain herniation is a condition in which a portion of the brain is displaced due to increased pressure—resulting in progressive damage to the brain—and is ultimately fatal. Usually, the brain herniation is a result of cerebral edema, which is the medical term for the condition of a swollen brain, usually caused by head injury. Elevated ICP is also caused by increased brain water content or other metabolic, traumatic and infectious conditions such as hypoxia, ischemia, brain hemorrhage, tumor and meningitis. Hypoxia occurs due to a lack of oxygen supplied to the brain, usually caused by cardiac arrest, leading to brain edema. Ischemia is the condition of deprivation of blood flow to the brain and leads to stroke because glucose and oxygen are not supplied to the brain. Ischemia is usually caused by formation of a blood clot (thrombus) and leads to the death of parts of the brain or ultimately of all the brain (cerebral infarction). Intracerebral hemorrhage is an increase in blood volume within the cranium, which is directly correlated with an increase in ICP. The main cause of intracerebral hemorrhage is a ruptured blood vessel in the brain resulting from a blow to the head or due to hypertension. The added mass of a brain tumor also causes an increase in ICP. In fact, an increase in ICP occurring without any head injury is often a sign of the presence of a brain tumor. Meningitis is a bacterial or viral infection of the meninges, a three-layer membrane surrounding the brain and spinal cord. Meningitis causes the meninges to swell and press against the skull and the brain. As a result, an intense pressure build up occurs notably raising the ICP. If not treated rapidly, meningitis leads to herniation. Therefore, measurement of the ICP is significant for detecting various neurological conditions. Furthermore, early detection of ICP variations is recognized as an important tool in improving a patient's condition or, ultimately, saving a patient's life. As well, monitoring the ICP is critical for identifying changes in a patient's pathological state.
At the present time accurate measurements of the ICP are only obtained using invasive techniques. However, the invasive techniques involve exposing brain tissue increasing the risk of infection, hemorrhage, and leakage of cerebral spinal fluid and, therefore, increasing the possibility of further aggravating a patient's condition.
Current state of the art non-invasive techniques for monitoring the ICP are not able to provide the accuracy, availability and usefulness of the invasive techniques. Non-invasive techniques include Computed Tomography (CT), Magnetic Resonance Imaging (MRI), Positron Emission Tomography (PET), Single Photon Emission Computed Tomography (SPECT), Transcranial Doppler ultrasonography (TCD), Transcranial Near-Infrared Spectroscopy (TNIRS), Ophthalmodynamomery (OMD), and impedance audiometry. Other non-invasive techniques have been recently disclosed in U.S. Pat. No. 5,951,477 issued Sep. 14, 1999 to Ragauskas et al. and in U.S. Pat. No. 5,388,583 issued Feb. 14, 1995 to Ragauskas et al. These techniques provide time delay estimation for measuring brain density variations—with the ICP variations being directly related thereto—by probing a patient's brain with ultrasound pulses of a specific frequency band. However, these techniques are inaccurate, ignoring dependency of brain density variations on a wide range of frequencies, and, therefore, disregarding information essential to accurately account for dispersive properties of a human brain.
It would be advantageous to provide a method and apparatus for non-invasive monitoring of brain density variations that is capable of replacing the invasive techniques. Furthermore, it would be highly advantageous to provide an apparatus for non-invasive monitoring of brain density variations in real time that is portable and easy to use.